The Global Three-Dimensional Structure for the Developmental Phase of ENSO A Thesis Presented in Partial Fulfillment of the Requirements for The Degree Masters of Science in the Graduate School of The Ohio State University By Scott Andrew Melaragno, B.A. Graduate Program in Atmospheric Science The Ohio State University 2010 Thesis Committee Dr. Jialin Lin, Advisor Dr. Jay S. Hobgood Dr. Jeffery C. Rogers Copyright by Scott Andrew Melaragno 2010 ABSTRACT An examination of NCEP reanalysis anomaly data for neutral El Niño-Southern Oscillation (ENSO) phases is conducted in order to portray a three-dimensional view of the global teleconnections associated with this phenomenon. The neutral phase, which occurs when Niño 3.4 sea surface temperatures (SSTs) lack either warm or cold anomalies, precedes both warm and cold ENSO events. Few studies have examined the significance of these phases, usually grouping both warm-to-cold and cold-to-warm phases into one mean state, when in reality these transitional periods are far from neutral. Because of a lack of neutrality seen within NCEP reanalysis data from 1950-2007, the title of ―developmental phase‖ will be given for apparent neutral events leading up to an extreme phase. During a developmental phase one year before a mature El Niño (December- January-February [-1]), warm SST anomalies bisecting the equator/date line and along 30°S within the eastern Pacific are seen. Increased SSTs also appear in the northern Pacific Ocean, southern Atlantic Ocean, Baffin Bay off the west coast of Greenland, Gulf of Mexico and the eastern Mediterranean Sea. Cold SST anomalies are seen predominantly throughout the Tropical Pacific. Enhanced precipitation and upward motion above warm SST anomalies occurs over the western Pacific, surrounding Indonesia and Papua New Guinea. ii Analysis of the zonal mean circulation provides a vertical representation of how the neutral phase affects the three latitudinal circulation cells, along with the horizontal Walker circulation. Symmetric cooling of the tropical troposphere and Northern Hemisphere (NH) midlatitudes can be seen during this phase, with a mid-level warm core above the equator. More vertical warming around the polar regions, especially in the Southern Hemisphere (SH) can be seen during the boreal winter one year before an El Niño. Combining these vertical and horizontal cross-sections shows a weakening and displacement of Hadley cells 20°N and S, with a strong westerly tropical jet positioned directly along the warm core in the mid-to-upper troposphere. Critical in the development and decay of ENSO events, the Walker Circulation appears to be deteriorating, a foretelling sign of an impending El Niño. Even in the polar regions, critical weakening of the polar vortex correlates with neutral conditions. The teleconnections seen during the neutral phases of ENSO provide new findings that help explain the complex dynamics associated with a coupled ocean- atmospheric system. The timescale of a developmental phase aids in predicting warm and cold events that are potentially one year away from fruition. With the completion of a three dimensional schematic and the corresponding teleconnections associated with a developmental episode, this study provides new methodology in forecasting extreme events throughout the entire ENSO cycle. iii DEDICATION Dedicated to my family, friends, and fiancé for their unconditional support through this two year adventure. I would not be where I am today without these people in my life. iv ACKNOWLEDGEMENTS I would like to extend my thanks to Jialin Lin for all of his help, guidance, and patience throughout the entire construction of my thesis. His introduction of the neutral phases of ENSO to me has proven to be an extremely interesting topic and an important area of future research. Also, special thanks to my committee members Jay S. Hobgood and Jeffery C. Rogers for their classes in Synoptic and Dynamic Meteorology. Their teachings concerning the physics and theories of the atmosphere have played an imperative role in this thesis. Additional thanks to Taotao Qian for her construction of the pre-1948 dataset and her help throughout this process. This work was supported by NASA Modeling, Analysis and Prediction (MAP) Program, NOAA Climate Prediction Program for the Americas (CPPA), and NSF grant ATM-0745872. The correlation analysis was conducted using online plotting tools developed by NOAA ESRL Physical Science Division (PSD), Boulder Colorado from their website at http://www.esrl.noaa.gov/psd/. Furthermore, a special acknowledgement to Erik Fraza, Mike Davis, and Meng- Pai Hung for all their support and advice in helping me complete this thesis. v VITA September 4, 1985 ....................................................Born USAFA, Colorado May, 2008 .................................................................B.A. Geography and Environmental Sciences, Miami University-Oxford FIELD OF STUDY Major: Atmospheric Sciences vi TABLE OF CONTENTS ABSTRACT........................................................................................................................ ii DEDICATION ................................................................................................................... iv ACKNOWLEDGEMENTS ................................................................................................ v VITA .................................................................................................................................. vi LIST OF FIGURES ........................................................................................................... ix Chapters 1. Introduction ............................................................................................................. 1 1.1 General and Historical Background of ENSO ................................................. 1 1.2 Post-TOGA Research and ENSO Theories ..................................................... 6 1.3 Global Circulation Cells during ENSO............................................................ 9 1.4 Unanswered Questions and the Purpose of this Study................................... 11 2. Data and Methodology.......................................................................................... 15 2.1 Data ................................................................................................................ 15 2.2 Methodology .................................................................................................. 16 3. The Neutral Phases of ENSO: Are They Really Neutral? .................................... 21 3.1 Results ............................................................................................................ 21 3.2 Summary and Discussion............................................................................... 24 vii 4. Global 3-Dimensional Structure of the Transitional Phase during Winter ........... 33 4.1 A Three-Dimensional View Using Zonal Mean Cross Sections ................... 33 4.2 A Global View Using Horizontal Anomaly Maps......................................... 37 4.3 Polar Stereographic Maps .............................................................................. 52 4.4 Presentation of Schematics ............................................................................ 56 5. Global 3-Dimensional Structure of the Transitional Phase during Summer ........ 72 5.1 A Three-Dimensional View Using Zonal Mean Cross Sections ................... 72 5.2 A Global View Using Horizontal Anomaly Maps......................................... 80 5.3 Polar Stereographic Maps .............................................................................. 96 5.4 Presentation of Schematics .......................................................................... 100 6. Summary and Discussions .................................................................................. 117 6.1 Key Findings ................................................................................................ 117 6.2 A New Methodology for Better Predicting ENSO ...................................... 120 6.3 Future Research............................................................................................ 120 REFERENCES ............................................................................................................... 122 viii LIST OF FIGURES Figure 1. The Oceanic Nino Index (ONI). Events are defined as 5 consecutive months at or above the +0.5o anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into Weak (with a 0.5 to 0.9 SST anomaly), Moderate (1.0 to 1.4) and Strong (≥ 1.5) events. For an event to be weak, moderate or strong it much have equaled or exceeded the threshold for at least 3 months (Image from The Climate Prediction Center (CPC) ENSO Impacts 2010). ............................................... 14 Figure 2. a) The raw Nino3.4 SST time series (thin line) and smoothed Nino3.4 SST time series (thick line), (b) the spectrum of raw Nino3.4 SST time series (black) and smoothed Nino3.4 SST time series (red), (c) the transition index, and (d) the lag-correlation between the transition index and the smoothed Nino3.4 SST time series. .................................................................................. 19 Figure 3. The (a) smoothed Niño 3.4 index and (b) the transition index. Both have the corresponding phases of ENSO, each lasting one year. ..................................